1. Field of the Invention
This invention relates generally to the field of semiconductor device manufacturing and, more particularly, to fault detection and control methodologies for ion implantation processes, and a system for performing same.
2. Description of the Related Art
There is a constant drive within the semiconductor industry to increase the quality, reliability and throughput of integrated circuit devices, e.g., microprocessors, memory devices, and the like. This drive is fueled by consumer demands for higher quality computers and electronic devices that operate more reliably. These demands have resulted in a continual improvement in the manufacture of semiconductor devices, e.g., transistors, as well as in the manufacture of integrated circuit devices incorporating such transistors. Additionally, reducing the defects in the manufacture of the components of a typical transistor also lowers the overall cost per transistor as well as the cost of integrated circuit devices incorporating such transistors.
Generally, a set of processing steps is performed on a lot of wafers using a variety of process tools, including photolithography steppers, etch tools, deposition tools, polishing tools, rapid thermal process tools, implantation tools, etc. The technologies underlying semi-conductor process tools have attracted increased attention over the last several years, resulting in substantial refinements. However, despite the advances made in this area, many of the process tools that are currently commercially available suffer certain deficiencies. In particular, such tools often lack advanced process data monitoring capabilities, such as the ability to provide historical parametric data in a user-friendly format, as well as event logging, real-time graphical display of both current processing parameters and the processing parameters of the entire run, and remote, i.e., local site and worldwide, monitoring. These deficiencies can result in non-optimal control of critical processing parameters, such as throughput, accuracy, stability and repeatability, processing temperatures, mechanical tool parameters, and the like. This variability manifests itself as within-run disparities, run-to-run disparities and tool-to-tool disparities that can propagate into deviations in product quality and performance, whereas an ideal monitoring and diagnostics system for such tools would provide a means of monitoring this variability, as well as providing means for optimizing control of critical parameters.
One technique for improving the operation of a semiconductor processing line includes using a factory wide control system to automatically control the operation of the various process tools. The manufacturing tools communicate with a manufacturing frame-work or a network of processing modules. Each manufacturing tool is generally connected to an equipment interface. The equipment interface is connected to a machine interface that facilitates communications between the manufacturing tool and the manufacturing frame-work. The machine interface can generally be part of an advanced process control (APC) system. The APC system initiates a control script based upon a manufacturing model, which can be a software program that automatically retrieves the data needed to execute a manufacturing process. Often, semiconductor devices are staged through multiple manufacturing tools for multiple processes, generating data relating to the quality of the processed semiconductor devices.
During the fabrication process various events may take place that affect the performance of the devices being fabricated. That is, variations in the fabrication process steps result in device performance variations. Factors, such as feature critical dimensions, doping levels, contact resistance, particle contamination, etc., all may potentially affect the end performance of the device. Various tools in the processing line are controlled in accordance with performance models to reduce processing variation. Commonly controlled tools include photolithography steppers, ion implant tools, polishing tools, etching tools, and deposition tools. Pre-processing and/or post-processing metrology data is supplied to process controllers for the tools. Operating recipe parameters, such as processing time, are calculated by the process controllers based on the performance model and the metrology information to attempt to achieve post-processing results as close to a target value as possible. Reducing variation in this manner leads to increased throughput, reduced cost, higher device performance, etc., all of which equate to increased profitability.
Ion implantation is a very complex and widely used process in the manufacture of integrated circuit devices. Ion implantation is a technique used to implant a dopant material, e.g., arsenic or boron, into a structure, e.g., a substrate, to form very precise implant regions having a certain dopant concentration and profile. Ion implantation processes may also be performed to implant dopant materials into a layer of material. Very precise control of ion implantation processes is desirable because of the impact the implant regions may have on the performance capabilities of the ultimate integrated circuit product. For example, precise control of the ion implantation processes performed to form the source/drain regions for a transistor or to control the threshold voltage of the transistor is required if the ultimate devices are to operate as intended.
Typically, in modern semiconductor manufacturing facilities, ion implantation processes are performed on a group or batch of substrates, e.g., wafers. The number of substrates processed in each batch may vary depending on the ion implant equipment used to perform the process. Most of the batch-type ion implant equipment may perform the ion implant process on 13 or 17 wafers at a time. There is great interest in attempting to insure that the processes performed in such ion implant tools are performed correctly. Moreover, in some cases, if the ion implant processes are performed incorrectly, the substrates subjected to such incorrect processes must be destroyed. That is, it is very difficult, if not impossible, to rework substrates subjected to erroneous ion implant processes.
In an effort to control ion implant processes, metrology data is taken after the ion implantation process is performed to determine whether the process has performed acceptably. Such metrology data may be acquired from production or test wafers. For example, TP420 and/or TP500 model metrology tools manufactured by Thermawave may be used to determine crystal lattice problems. As another example, a Prometrix model number RS55 metrology tool may be used on test wafers to determine the dopant concentration profile of implanted regions after the implant process is performed. In some cases, the metrology data may be acquired using a secondary ion mass spectrometry (SIMS) tool made by Cameca on test wafers. However, such processes may take a relatively long time, e.g., for sheet resistance data, the process may take approximately 10 minutes per substrate to perform such metrology tests. Moreover, such metrology tests are typically not performed until well after the implantation process has been completed, e.g., hours or days after the ion implantation process is finished. As a result, the metrology data is not provided in as timely a fashion as would otherwise be desired. For example, during the period when metrology data is being obtained, additional substrates may be processed in the ion implant tool using tool parameters that are producing implant regions of an undesirable quality.
As stated previously, ion implantation processes are very complex, and the successful performance of such ion implantation processes depends on a number of related parameters of the process, e.g., implant dose, implant energy level, gas flow rates, the current and voltage levels of the filament, ion beam current, number of scans, etc. To achieve a desired to targeted result, modem ion implant equipment may automatically adjust or tune the ion beam prior to performing an implant process in an effort to insure that the implant process performed by the tool will produce acceptable results. That is, the ion implant tool attempts to tune or adjust a plurality of these related parameters such that a selected combination of these parameters will produce the intended results. The tuning process is a relatively time-consuming process. This internal tuning is typically accomplished by directing the ion implant beam at a Faraday cup within the implant tool and varying one or more of the tool parameters. Unfortunately, as target conditions or values change, as new ion implant recipes are performed and/or as the volume of substrates processed by a tool mounts, the process may become less stable, thereby potentially introducing errors into the ion implant process. As a result, the resulting implant regions, and the devices comprised of such implant regions, may be less than desirable in terms of performance.
Moreover, the tuning process described above is typically performed whenever the ion implant tool is to perform a new implant recipe. Given the vast number of tool parameters that may be varied to achieve the targeted implant region and process, the tuning process may produce a vast number of combinations of such parameters, even though the target implant region and process are the same. As a result, effective monitoring of such ion implant tools and processes are difficult.
What is desired are systems and methods that enable effective monitoring and control of ion implant tools and processes in a timely manner. The present invention is directed to methods and systems that may solve, or at least reduce, some or all of the aforementioned problems.